implement optional match short-circuiting for pluggable matchers
Merge pull request #9 from lastobelus/short_circuit_matchers

Matchers need to be able to short-circuit evaluation
simplify code around should_match?
remove trailing white spaces
explicitely break with false when should_match?
let matches? return true, false or :break
remove unused class in test
Merge branch 'simpler_should_match'